Hydraulic transmission of the swash plate type pump and motor, and control mechanism therefor



March 11, 1952 s, Q MOON 2,588,866

HYDRAULIC TRANSMISSION OF THE SWASH PLATE TYPE PUMP AND MOTOR, ANDCONTROL MECHANISM THEREFOR Filed Sept. 14, 1944 3 Sheets-Sheet llNl/ENTOR; STERLING C MOON,

l I HI H H l l hl h" H. U I I IH March 11, 1952 s, c MQQN 2,588,866

HYDRAULIC TRANSMISSION'OF THE SWASH PLATE TYPE PUMP AND MQTOR, ANDCONTROL MECHANISM THEREFOR- Filed Sept. 14, 1944 s Sheets-Sheet 3 00mJOE .FZOU

nmokoiv I INVENTOR," STERUNG Cf MooN, BY

HTT'Y March 11, 1952 s. c. MOON 2,538,366

HYDRAULIC TRANSMISSION OF THE SWASHPLATEMTYPE PUMP AND MOTOR, ANDCONTROL. MECHANISM THEREFOR 3 Sheets-Sheet 3 Filed Sept. 14, 1944I/YVENTOR, jTERLlNG C. MOON,

jpaw/ Patented Mar. 11 1952 HYDRAULIC TRANSMISSION OF THE SWASH PLATETYPE PUMP AND MOTOR, AND

CONTROL MECHANISM THEREFOR Sterling 0. Moon, Worthington, Ohio,assignor, by mesne assignments, to The Jeffrey Manufacturing Company, acorporation of Ohio Application September 14, 1944, Serial No. 554,125

10 Claims.

This invention relates to a truck and to a hydraulic transmission.particularly adapted for use in a truck but which may have other uses.

An object of the invention therefore is to provide an improved drivemechanism for a truck including particularly a manually controllablehydraulic transmission which provides the truck with desirablecharacteristics,particularly in that it automatically operates toproduce a maximum torque at a low speed whenever a great resisting forceis encountered. It may be stated that the truck is particularly usefulas a truck .of a coal loading machine, but it vmayhave other importantuses, such as being a truck of a mining machine, mine locomotive, or amine shuttle car .or any other truck in which the speed is reducedautomatically whenever a large resisting force is encountered, therebeing amaximum torque produced at a minimum speed.

A further object of the invention is to provide ahydraulic transmissionin which the fluid-out put of the pump is preferably reversible bymanual control without reversing the direction .of rotation of the pumpand in which the output of the pump .is variable preferablyautomatically in response to .the output pressure thereof and also inthe complete embodimentof my inven tion in which the motor of thehydraulic transmission has a variable displacement v.per revolutionwhich increases from a minimum displacement at relatively low pump"output pressures to a maximum displacement at the highest pump outputpressure.

A further object of the inventionis 'to provide an extremely flexibleand automatic hydraulic transmission including a hydraulic pump drivinga hydraulic motor.

'corporating the hydraulic transmission of my invention;

Figs. 2 and 3 together show in detail the 'hydraulic transmissionincluding the piping diagram therefor;

Fig. 4 is a plan view of the hydraulic transmission;

Fig. 5 is an'elevationalview thereof; and

Fig. 6 is a detail sectional view taken on the line 6-5 of Fig. 2,looking in the direction of the arrows.

The truck illustrated in Fig. l of thedrawings is disclosed in morecomplete detail and. claimed in the patent of Arthur L. Lee, No.2,395,333,, for a Mine Truck, issued February 19, 194:6, .and it is tobe understood that unless a contrary fact is indicated, the structurethereof follows the disclosure of that application.

The truck includes a main frame I0 which is supported upon four wheels 1I, all of which may be driven and steered. Mounted on the main frame i0is an electric motor I2, the rotaryshaft t2 of which extends forwardlytherefrom, and through a bevel pinion M which meshes with a bevel pinionit which is keyed :to a shaft Iii (see Fig. 2) of a pump I? of thehydraulic transmission which as a unit is designated [8.

As hereinafter described more completely, the hydraulic fluid output ofthe pump ii is delivered to a motor lfiof the hydraulic transmission,the rotary shaft 26 (see Fig. 2) of which drives a pinion 2! which isconnected by agear "train .22 to differentials 23 and 24 mounted onopposite sides of the main frame it] which in turn are driven through adifferential 25. Universal Joint mounted drive (shafts 2'6 extendforwardly and rearwardly on opposite sides of the main frame it), therebeing four such drive shafts, one connected to driveeach of the wheelsII, all as disclosed in more detail in the above-mentioned Patent No.2,395,333.

The truck illustrated may be used for a variety of purposes, but thehydraulic transmission may be used with a variety of trucks and hascertain characteristics which make it particularly desirable for suchdevices as loading machines, mining machines, mine locomotives, andshuttle cars employed in underground coal mines. For

example, in a loading operation the loaderis fed slowly into a pile ofcoal and there is an. appreciable resisting force against which theloader must be pushed to effect the gathering of coal. It is desirablethat the feed rate of the loading machine be such as not to overload theunit and yet be such as to maintain a high elliciency of operation atall times.

The hydraulic transmission which I have provided operates automaticallyto feed the truck at a maximum speed consistent with a non-overloadingcondition, but Whenever high resisting forces, or, in other words, heavyloads, are encountered the hydraulic transmission operates automaticallyto reduce the feed rate, while at atsasce the same time increasing thetorque or pushing force so that the machine will not overload or stallbut will continue to feed itself into the material at whatever rate theresisting force die tates; the transmission being such as to produce amaximum torque at minimum or zero speed. This is an extremely desirablecharacteristic in loaders, mining machines, mine locomotives and shuttlecars, and it is a characteristic which may find useful application inother machines, vehicles or the like. Because of this fact it is to beunderstood that the hydraulic transmission, in certain broader aspectsof my invention, may have a general use, though in its more specificapplication it is particularly useful in mining machines of theabove-mentioned type.

Referring first to Figs. 4 and 5 of the drawings, it will be noted thatin the hydraulic transmission it the pump ii and the motor 19 arephysically bolted together by bolting their housings as a unit, and alsobolted to the housing of the pump ll is a valve unit iii, the structureof which is illustrated in detail in Fig. 3 of the drawings.

Referring to the detailed structure of the pump ll as illustrated inFig. 2 of the drawings, said pump is generally of standard constructionand is of the longitudinal or axial piston type employing a swash plate,it being modified, however, in certain particulars to perform thefunctions desired as above outlined. Said pump includes a housing orcasing 22 within which is a port plate 29 of conventional structure,which may follow, for example, that disclosed in the patent to Robert K.Jefirey, No. 2,331,694, dated October 12, 1943.

The port plate 29 has feed and exhaust ports, not illustrated, whichcommunicate with feed passageways 38 and 3! formed in the head plate ofthe casing or housing 28. Since the pump I! is reversible by adjustingthe swash plate to either side of its neutral position as hereinafterdescribed, the passageways 3t and ti may selectively be pressure andreturn passageways. As illustrated in Fig. 2 of the drawings, passageway3! is the pressure passageway.

Within the housing 28 is mounted a rotor 32 carried on the previouslymentioned shaft it, which shaft 56 is mounted adjacent opposite ends inanti-friction bearings 33 and 3d. The rotor 32 carries a plurality ofaxial pistons 35, the outer ends of which are beveled and bear againstan anti-friction mounted thrust plate 3G mounted on a pivoted swashplate 3'? pivotally mounted to the casing 2 3 about a central pivot ortrunnions 38.

On opposite sides of the axis of pivot or trunnions 38 the swash plate31 carries antifriction rollers 39 and it, the former of which bearsagainst the outer end of a piston ii, and

the latter of which bears against the outer end of a piston rod 12having a piston t3 mounted on its lower end, as viewed in Fig. 2 of thedrawings.

Piston i! is carried in a cylinder i i mounted in the housing 28 which,as hereinafter described more completely, is subject to the pressure ofthe hydraulic fluid delivered at the output of the pump ll. Thisprovides a continuing force on the swash plate 37, tending to rotate itin a counter-clockwise direction as viewed in Fig. 2

of the drawings. In opposition to this force the piston 43, which ismounted in cylinder is formed as a part of the housing 2.8, exerts alarger force whenever hydraulic fluid is applied to it, since it has agreater area.

As a consequence, the angular position of the swash plate 3? can beadjusted so that the slice tive plane thereof, which is the plane of thesurface of thrust plate 36, can be varied through a plurality ofpositions. For example, if the plane of thrust plate 36 is perpendicularto the axis of the shaft it, the pistons 35 will not reciprocate at allas the rotor 32 and shaft it are rotated.

With the parts as illustrated in Fig. 2 of the drawings, it is evidentthat the plane of the swash plate 3? and the thrust plate 36 are rotatedslightly counterclockwise to a plane perpendicular to the axis of shaftit and consequently as the rotor 52 and shaft is rotate, the pistons 35will reciprocate and hydraulic fluid under pressure will be delivered tothe passageway 35,

passageway 36 under these conditions being the return or suctionpassageway. Obviously the volumetric output of the pump ll may be variedby adjusting the angle of the swash plate 3? and thrust plate 36 withrespect to the axis of shaft The pump output will be at maximum whenthis angle is the greatest and at minimum when the plane thereof is atright angles to the axi of shaft l5. Furthermore, the direction of fiowof the hydraulic fluid from the pump i! will be reversed, while theshaft it rotates always in the same direction, depending upon whetherthe plane of the swash plate 3i and thrust plate 36 is rotated in aclockwise or counter-clockwise direction from said right angle position,the volumetric output per revolution being dependent upon this angle.The pistons or rods ii and 42 will lock the swash plate 3? in position,the position bein determined by the position of the piston it ashereinafter described more completely.

To control the direction of the hydraulic fluid output from the Pump llas well as the volume thereof per revolution, I provide controlmechanism which does not act directly to adjust the swash plate 37, butwhich acts through a manual adjustment so as to set up a selected fluidpressure to be reached by the hydraulic fluid delivered by pump ll, andthe pump operates automatically to adjust its volumetric output so as toproduce and substantially maintain this selected pressure.

To this end I provide a control rod 46 which may be operated by anydesired operating mech-,- anism, which rod extends into a shiftable cageor shell tl mounted for reciprocation in a housing extension 48preferably formed as an integral part of the pump housing 28. The rod 46slides through spaced. sleeves 49 and 50 which receive a coil spring 5i,tending to force the sleeves t9 and 56 apart, said sleeves 49 and 50being held in the cage l'l by snap ring abutments 52 and 53. The sleeve49 abuts an enlargement 54 on the rod 46, and the sleeve 50 abuts a nut55 thereon.

It is obvious that if the rod 46 is moved in either direction from thatillustrated, it will compress the spring 5l, the force of which will betransmitted to the cage 4i, tending to move it in the direction in whichrod ie is moved. Rod 46 can be moved to either side of its neutralposition and the ultimate result will be to shift the swash plate 31from a maximum position in one direction through the neutral position toa maximum position in the opposite direction, thereby producingselectively any desired pressure on the output passageway of pump ll.

As best seen by reference to Figs. 2 and 6 of the drawings, cage i! isprovided with a boss 56 on which a yoke 51 is pivoted by a pin 58. The

lower end of the yoke 51 extends into a recess in the piston rod 42where itprovides a pivotal connection therewith. (See Fig. 6.) Thebifurcated upper ends of the yoke 51 are connected to shift rods 59,which are pivoted at opposite sides of an operating block 66 (Fig. 2) ofa control piston 6| mounted in a cylinder or bore 62 formed in thecasting which provides cylinder 45.

The cylinder 62 is provided with a peripheral chamber 63 whichcommunicates by way of passageway or bore 64 with the lower end ofcylinder 45, as viewed in Fig. 2 of the drawings. The piston or spool 6|is provided with a land 65 having an axial dimension adequate to coverthe peripheral chamber 63. Above land 65 the spool or piston 6| is ofreduced diameter and leads to a bore 65 therein which extends throughthe block 66 and communicates with the interior of the housing 48 which,as clearly illustratedin Fig. 6 of the drawings, is in directcommunication with the interior or" housing 26, all of which isconnected by a drain pipe or conduit 61 which returns to a hydraulictank 68 (see Fig. 3 of.

the drawings).

Extending to the bottom of the peripheral chamber 63 of cylinder 62 andleading to said cylinder 62 is a bore 69 formed in the casting whichprovides the cylinder 62 and cylinder 45, which bore 69 is connected toa pressure control pipe or conduit 16, which pipe or conduit 76 carrieshydraulic fluid under pressure at all times, which pressure is the sameas the pressure delivered by the pump I1 regardless of its direction ofdelivery, as hereinafter described more com pletely. In other words, thehydraulic pressure in conduit 16 represents the pressure in the system.This conduit is always a pressure conduit. As hereinafter described,hydraulic fluid under pressure is derived. from said conduit to controlboth the pump and the motor as well as certain other devices, includingthe braking action of the motor I9.

As illustrated in Fig. 2 of the drawings, the pump I! has its swashplate 3'! in position to deliver hydraulic fluid under pressure to thepassageway 3|, with the passageway 36 acting as the return. The controlparts including the rod 46 and parts operated by it, are illustrated ashaving been moved downwardly, thereby to increase the pressure deliveredto the passageway 3|.

This increased pressure is effected by increasing the hydraulic fluiddelivery to the motor, which tends to increase its speed and theincreased speed will tend to build up its pressure which is reflectedback to the control apparatus for the pump. In other words, the amountof fluid delivered by the pump to the motor I!) for any setting of thecontrol rod 46, will automatically he at the volume or rate which buildsup and maintains the preselected pressure. For example, should thevehicle encounter easy travel, its speed will automatically increase tobuild up the predetermined pressure determined by the setting of controlrod 46. On the other hand, should the vehicle encounter a higherresisting force, the volume will automatically decrease to maintain thepreselected pressure in the line '16.

This is effected by the following operations. With the rod 46 moveddownwardly, as illustrated in Fig. 2 of the drawings, it will transmit aforce to the spring 5| which in turn will transmit a force to the shell41, and in the absence of some holding force the shell 41 will movedownwardly as illustrated and thus move its pivot pin 58 downwardly.Since the-yoke 5-1 is pivoted to the rod 42, which is stationary for themoment, the pivoting of the yoke 51 will move its lower end downwardlyand through rods: 59, shift the spool or piston 6| downwardly so thatland uncovers the peripheral chamber 63. Under these conditions, thecylinder '45 below the piston 43 will be drained to the interior of thehousing or casing 28 through bore '64, uncovered chamber 63 and bore 66which communicates with the interior of housings 48 and 28.

Pressure in the control circuit or conduit 10 is always applied to thepiston 4|, tending to rotate the swash plate 31 in the counter-clockwisedirection, and this release of hydraulic fluid ahead of piston 43 willpermit such counterclockwise rotation of the swash plate 67. Thismovement will, of course, swing the yoke 5'! about its pivot 58, whichthrough the rods 59 will move the spool or piston 6| upwardly so thatland 65 covers the chamber 63, sealing off the above-describedpassageway and again locking the piston 63 in position.

As previously mentioned, the pressure of the hydraulic fluid output ofpump l1 and thus the pressure in the control conduit 10 is determined bythe position of the rod 46. The rod 46 also controls the direction ofthe hydraulic flow from pump H so that either passageway 30 or 3| may bethe pressure passageway. Thus both the direction and the volume of thehydraulic fluid pressure delivered by pump |1 may be controlled, andthis pressure is automatically determined for each position of thecontrol rod 46.

To effect this automatic operation, when rod 46 is moved to any positionexcept that which would put the swash plate 3'! in neutral, thetendency, of course, is for the spring 5| to transmit directly anymovement of the rod 46 to the shell 41. However, the spring 5| providesan impositive connection between rod 46 and shell 41. Shell 41 issubject to centering forces which measure directly the pressure of thehydraulic fluid in the system, namely the pressure in conduit 10 whichis the pressure delivered by the pump I! and received by the motor 9.Consequently, the shifting of the swash plate 3'! will be adjustedautomatically so that the pressure in the system is determined by theposition of rod 46. For example, if rod 46 is adjusted as abovementioned to change the angle of the swash plate 31, thereby to increasethe volume of the hydraulic flow from pump I! to motor Hi, the tendencywould be for the pressure to increase if the motor I! encounters thesame load due to its increase in speed.

This pressure in line 16 is delivered to two centering pistons II and 12which are mounted in cylinders or bores formed in the casing 28, saidcylinders H and 12 being positioned on opposite sides of the boss 56 ofshell 41. The pistons H and 12 have enlarged heads 13 and 14,respectively, so that at their maximum extended positions their headsstrike abutments on their cylinders, and the dimensions of the parts aresuch that when both said heads strike said abutments, said cage 41 andboss 56 will be in their central positions.

The cylinders which receive the pistons H and 12 both derive hydraulicfluid under pressure from conduit 10 and consequently the centeringforce delivered to the shell 41 through the. boss 56 by the pistons H or12 will necessarily match the force developed by the spring 5| caused bymovement of rod 46. Piston II will supply this centering force if rod 46is moved upwardly from its normal or released position. Piston 12 willsupply this centering force if the rod 46 is moved downwardly from saidneutral position. Once the rod 46 is moved to a desired position andheld there, the pressure in the system will be maintained at apredetermined value determined by the position of the rod 49, and toeffect this the shell 4! is free to move against pistons II or 12 as thecase may be, to shift the spool Bl which in turn shifts the swash plate31 to control the output of pump I1 so that its rate of fluid deliveryis such that, considering the opposition to rotation set up by the motorl9, it insures said predetermined pressure. v

It is thus to be particularly noted that the control rod for pump lldoes not control directly its volumetric output per revolution, but onthe other hand controls through a wide range the pressure of thehydraulic fluid delivered by said pump, and the volume of the pumpautomatically accommodates itself to maintain this preselected pressureas determined by the resistance to movement which the motor I9 offers.

Attention is now directed particularly to the construction of the motorl9 which in many particulars follows closely that of the pump, but whichincludes certain important differences which shall be pointed out. Itmay be mentioned that unless a contrary fact is indicated, the structureof the motor i9 is the same as the pump H.

The motor i9 includes a casing or housing 19 containing a port plate itwhich communicates with the passageways 39 and 3! which are common withthe pump passageways 99 and 3! since in the actual construction thesepassageways are a continuation between the pump and the motor, beingformed in the head castings of each of them which are bolted together,as clearly illustrated in Figs. 4 and 5 of the drawings. It is for thisreason that they are given the same reference characters on both thePump and the motor.

Within the housing is a rotor ll having a plurality of axial pistons 79which bear against a thrust plate 99 mounted in anti-friction bearingsin an adjustable swash plate 99. The swash plate 89 is mounted on spacedtrunnions or pivots 8|, on opposite sides of the axi of which areanti-friction rollers 82 and 93 bearing on the outer ends of piston 94and piston rod 85, respectively, said piston rod 85 carrying a piston 89movable in a cylinder 8'! formed as a part of the housing '55.

The piston 99 extends into a cylinder 88 attached to and forming a partof the housing 75 and connected to the pressure conduit 19 so thatpiston 84 is always responsive to the pressure of the hydraulic systemand tends to swing the swash plate 89 in a counter-clockwise directionagainst the piston rod 95 which co-operates therewith to lock it inadjusted position.

It may be noted that the piston 94 is longer than the similar piston 9|of the pump. This is because the swash plate 3? 'of the pump is adaptedto swing to opposite sides of the zero output position of said pumpwhich is the position in which its plane is set at right angles to theaxis of shaft It. The motor l9, however, preferably has a minimumdisplacement so the plane of the swash plate 99 as well as the thrustplate 19 i never exactly perpendicular to the axis of shaft 29.Furthermore, the plane of said swash plate 89 can only swing in acounterclockwise direction from a near perpendicular relation to theaxis of shaft 29. Asa cofise quence, the motor l9 always rotates in thesame direction, provided the fluid flow to it is in the same direction.It is reversed by reversing the 5 direction of the fluid fiOW to it,which is effected by the pump H as above described.

The motor casing 15 is provided with an extension 89 which receives acage or shell 99 similar in construction to the pump shell 9'1. Shell 99has a boss 9i upon which is pivotally mounted a bifurcated yoke 92 oneend of which extends into and has a pivotal connection with the rod 85,the opposite bifurcated ends of which are connected to rods 93 which arepivotally connected to a block 99 of a piston or spool 95 workin in acylinder or bore 96 formed in the housing portion which providescylinder 81.

The cage 99, boss 9|, yoke 92, rods 93, block 94, spool 95 and cylinderor bore 99 are duplicates of the shell 41, boss 56, yoke 51, rods 59 andspool 9| and they operate in substantially the same way to control theactuation of piston 86 as the corresponding pump parts control theactuation of piston 93. It is therefore believed unnecessary to describein further detail the other associated parts, particularly of the spool95, since it functions to adjust the piston 86 and thus adjust inresponse to pressure the volumetric displacement per revolution of themotor l9 or, in other words, its speed of rotation for any given rate ofhydraulic fluid delivery to it.

The mode of control, however, of the shell 99 differs from that of theshell 41, which I shall now describe. For example, shell 4? iscontrolled through a spring 5| under the opposing influences of thecontrol rod 46 and the centering pistons H and 12. Shell 99, however, iscontrolled by the opposing influences of a coil spring 91 and a singlepiston 98 which is contained in a bore or cylinder provided in thecasing 15, which is subject to the pressure in the system since it isconnected to conduit 10. The spring 97 functions so that it tends toswing the swash plate 99 always in a clockwise direction, thus tendingto decrease the volumetric capacity per revolution of each piston andcylinder of the rotor 17, or, in other words, to increase the speed ofshaft 29 for any given quantity of hydraulic fluid delivered thereto. 7

The piston 98 tends to control the shell 99 so that it acts through thepiston 86 and its controlling spool 95 to overcome this tendency of thespring 97 or, in other words, in response to pressure in the conduit 19to increase the volumetric displacement of the motor I9 per revolutionand thus to decrease the speed of shaft 29 for any given rate ofhydraulic fluid delivered thereto.

The action of the spring 91 and the counter action of the piston 98controlling the spool 95 either to drain the cylinder 81 or to deliverhydraulic fluid to it, operate as follows. Spring 91 is held betweenplugs 99 mounted on opposite sides thereof in shell 99 and held betweensnap rings I99 on opposite ends of said shell 99. The bottom plug 99abuts a pin l9l which in turn abuts the head of cylinder 81 which is apart of the casing or housing 15. Spring 97 therefore urges rotation ofswash plate 89 in a clockwise direction. Pressure in the control conduit19 is delivered to the cylinder containing piston 98 and urges itdownwardly, as viewed in Fig. 2, or in opposition to the action ofspring 91, thus urging the swash plate 89 in a counter-clockwisedirection which tends to increase its volumetric passageways 3| and III]act on piston I22, tending to move the piston II6 downwardly. Whenpiston I I6 is in its neutral position as illustrated, passageways III]and III are isolated. However, if said piston II6 moves eitherdownwardly or upwardly in response to an excess pressure in passagewaysBI and III) or 30 and III, respectively, said passageways IIO, III willbe interconnected through the hollow piston I I6 and radial ports I26located on opposite sides of the partition I23 in a manner which isobvious from Fig. 3 of the drawings.

It is evident that this movement of the piston I I6 will be by virtue ofthe hydraulic pressure on piston I22 overcoming the compression ofspring I I8, or the hydraulic pressure on piston I25 overcoming thecompression of spring H1. The springs H1 and H8 are preferably identicaland can be overcome to provide the relief valve characteristic at anydesired pressure, such as 1800 pounds per square inch.

To provide the braking action of the motor I9 whenever the Vehicle istraveling under its own power so as to drive the motor I9 as a pump, Iprovide an apparatus which I shall now describe. This braking action, ofcourse, will take place only when the control rod 46 is in its neutralor zero position, in which the swash plate 31 of pump I1 is in itsperpendicular position with respect to the axis of shaft I6. Under theseconditions, the action of the pump I1 is the same as though passageways30 and 3! were shut off by valves, since they are blocked at said pump.It is necessary to disconnect effectively the braking mechanism exceptwhen the control lever 45 is in its neutral position. Otherwise, thebraking mechanism would act as a relief valve and discharge thehydraulic fiuid into the tank whenever its set pressure was exceeded,and in practice its set pressure is about 400 pounds per square inchwhich is considerably below the maximum operating pressure of thesystem.

Associated with the control rod 46 of the pump I1 is a piston I21 whichslides in a cylinder I28 formed in the casting which provides forcylinder 45 and which at its approximate center is providedwith anintegrally projecting ring I29 which has close contact with the pistonI21. The ring I29 is provided at its center with a peripheral chamberand when the rod 46 and the piston I21 are in their normal or neutralpositions, this peripheral chamber aligns with radial bores I30 in thepiston I29, which communicate with a longitudinal bore I3I therein,which adjacent the top of cylinder I28, as viewed in Fig. 2, is alsoprovided with radial bores. An attaching clip I32 is provided to connectremovably the rod 46 and piston I21.

The cylinder I28 is formed in part in the casting which provides forcylinder 45, as above mentioned, and in addition is formed in part in acylinder extension 233. That portion of cylinder I28 below the ring I29is connected to drain by being connected to the interior of housingextension 48 b means of bore I33.

The peripheral chamber in the ring I29 is connected to the controlconduit 13. A brake line or pipe I34 extends into the cylinder I28between the ring I29 and the top or head of said cylinder.

It may be pointed out here that whenever the vehicle is traveling so asto drive the motor I9 as a pump, that that passageway, conduit or port30 or 3I into which the motor I9 is discharging hydraulic fluid will beconnected to the control 12 conduit 10 through the pressure shiftablevalve I02.

When control rod 46 is in its neutral position, the piston I21 will bein the position illustrated in Fig. 2 of the drawings. Under theseconditions the hydraulic fluid under pressure in the control conduit orcircuit 10 will flow through the chamber in ring I29 through the radialbores I30 to the longitudinal bore of piston I21, then on to the radialbores near the top of the longitudinal bore I3! to the cylinder I28 andthen. by way of brake line or pipe I34 to a cylinder I35 (see Fig. 3)formed in the bottom head of that portion of the valve 21 whichconstitutes the brake valve. The cylinder I 35 is provided with a pistonI36 which abuts the bottom of a large control piston I31 having spacedlands I39, I39 which have a close fit with a cylinder or bore I40 formedin the block II2.

Between the land I39 and the top head of the brake valve mechanism is acoil spring I4I through which a guide I42 extends, said guide projectingthrough the top of said brake valve. As clearly illustrated in thedrawings, the land I39 normally isolates the pressure and returnpassageways H0 and III. However, if a predetermined pressure isdelivered to the brake line I34 sufficient to overcome the downwardforce developed by spring I4I, the piston or spool I 31 will be forcedupwardly and provide a bypass connection between the passageways H0 andIII or, in other words, between passageways 30 and BI.

Under the assumed conditions, the motor I9 was acting as a pump, itbeing driven by the vehicle rolling down hill or being pushed. Since theoutput of the motor I9 acting as a pump can not be delivered to pump I1because its swash plate is in the perpendicular position, this fluid hasto go somewhere and as soon as the pressure in control conduit I0 isbuilt up to a predetermined pressure, such as 400 pounds per squareinch, the valve I31 is actuated to allow the output of motor I9 to bedelivered to the input passageway thereof, thus circulating thehydraulic oil through the braking valve I31, I40. This provides anautomatic predetermined amount of braking action.

In order to increase this braking action above the minimum which isautomatically determined, I provide a brake lever I43 which is pivotedat one end to a bracket I44 and which carries an anti-friction rollerI45 adapted to roll on top of the projecting guide I42. Obviously, bypushr ing downwardly on the brake lever or handle I43, the brakingaction may be increased since this force will be added to that of thespring I4I which must be overcome by the pressure in the brake line I34before the motor I9 acting as a pump will be relieved.

The engine I9 has been designated as a motor because in the hydraulictransmission it normally acts as such. However, as above mentioned, it,under certain circumstances, will act as a pump. Thus it is genericallydesignated as an engine, the same as the pump I1 might also bedesignated as an engine since it could operate as a motor, though in mysystem it is not so employed.

To review briefly the operation of the hydraulic transmission, power isdelivered to shaft I6 of pump I1 and power is delivered from shaft 20 ofmotor I9. The manner in which shaft I6 is driven and in which shaft 20drives the vehicle, need not be repeated.

If control rod 46 is released, it assumes a norcapacityper revolutionand thus decrease its speed for any given volume of hydraulic fluid.

The spool 95 is shown moved downwardly from its neutral or normalposition and thus is shown as-draining the cylinder 8?, which means thatthe pressure in line Til has acted through piston 98 to overcome thespring d? to actuate piston 86 in a manner to swing the swash plate in acounter-clock-wise direction. The spring Si is preferably pre-loadedsothat a pressure of approximately 500 pounds per square inch is requiredinLline 70 before swash plate til is moved from its minimum-position.

It is, of course, obvious that as seen in Fig. 2 of the drawings shouldthe pressure in conduit 10, for'example, decrease below that at whichthe swash plate of pump I; is held, the spring 51 will urge theassociated shell ll downwardly because the resisting or balancing effectof the piston 12 will bereduced. The downward movement of the shell 41will move piston 6! downwardly and place cylinder 45 in communicationwith-the tank '68. Piston d2-t8 will be moved downwardly by piston lluntil it, operating through the yoke '5? and rods 59, causes the piston6l'to close the chamber 63, thereby isola ing the" cylinder 45 from thetank. Downward movement of the pistond3, of course, is accompanied bycounter-clockwise movement of swash plate37 which causes the outputvolume ofpump l1 tonincrease.

When the pressure in line it decreases below that at which the swashplate iii of motor 59 is helchthe spring-Bl will urge the shell 9%upwardly because. the resisting or balancing effect of the piston9'8'is' reduced, Upward movement of the shell 90 will lift piston 95 toconnect cylinder ill to the. line 70 through bores or passagewayssimilar to bores or passageways lit and E9 of pump ll. Piston 86' willmove upwardly until it, acting through yoke 92 and rods 93, moves thepiston 55 downwardly to seal the cylinder 8? from the conduit 10. Upwardmovement of piston d5, of course, adjusts the swash plate sii'towardmin: imum position. Should the pressure in conduit llli'norease abovethat for which the swash plates 3! and B are set, the above describedoperations would be reversed. Thus when the pressure in conduit ll!decreases below that for which the swash plates Sland Eli are adjustedthe output volume per revolution of pump ii is increased and the inputvolume per revolution of motor Il9is decreased, and when the pressure inconduit 10 increases above that for'whicn the swash plates 31' and 80are adjusted, the output volume per revolution of pump i'i is decreasedand the input volume per revolution of motor i9 is increased; Theforegoing example not to infer that these, actions always take placetogether,

but since the action is similar in both instances whenever the conditionis realized in the pump or the motor, the comparison is believed to bein the interest of clearness.

As previously mentioned, the control conduit ll! is: always suppliedwith hydraulic fluid under pressure, regardless of whether passageway3%! or 3| isthe pressure passageway. To this end a selector valve ill?is provided, which includes a cylinder connected at opposite ends to thepassageways 3i; and 3! as'illustrated, and provided with a floatingpiston N3, the opposite heads or" w hich'are subjecttothe pressure ofthe passage-'- ways 30 and 35. If passageway Si is the pressurepassageway as illustrated, piston i t3 will be moved downwardly, as-illustrated,- and. the hydraulic fluid under pressure'will flow throughpassageway 3! to conduit 70. Piston I03 under these conditions willblock passageway from passageway Ml. Should passageway 3d become thepressure passageway piston I iit'will move upwardly, as viewed in Fig.2, blocking the previous connection between passageway 31 and conduitl6. and interconnecting passageway Bil and said conduit Ill.

In Fig. 3 of the drawings I have illustrated a supercharging pump HMwhich derives hydraulic fluid from the tank 68 and delivers it to thepassageway 89 or 3!, depending upon which is the suction or returnpassageway as hereinafter described. The output of the pump M34 isdelivered to the combination reducing, relief and brake valve designatedgenerally El. I also pref delivering the reduced pressure to apassageway H31; Passageway Ill! communicates by means of ball checkvalves its and Hill with passageways H0 and Hi, respectively, which areformed in the housing, casing or main block l min valve 2'1 and areconnected to the If passageway 35 is the pressure passageway,

it will maintain check valve l as closed and permit the output of pumplM'from the reducing valve N56 to enter passageway 39 through checkvalve,

Hi9. If a reverse condition exists, said output of pump EM would bedelivered to passageway 3!.

In addition, a certain amount of hydraulic fluid in passageway it! frompump l M is metered through a passageway M3 to a passageway llll whichleads to the port plate 25 and bearing 33 of the pump ll, discharginginto the interior of the casing 2s which is connected to drain. Thefunction of this oil is to provide a cooling fluid, particularly for theport plate 29 of the pump H which is the element which tends to generatethe most heat during operation of the pump. This cooling device forthepump ll is an important feature of my invention and obviously maybeemployed in hydraulic pumps generally. The cooling device abovereferred to is claimed in my Patent No. 2,554,047, dated May 22, 1951,for Hydraulic Engine Cooling and Lubrieating System and Apparatus.

The relief characteristic of the combination valve 2? is provided byvirtue of a cylindrical bore .1 l5 formed in the body or block H2, inthe central portion of which is a composite piston l i 6 which isnormally held in a central position, as

illustrated in Fig. 3 of the drawings, by. means of a pair of coilsprings. I i! and i l 8 which surround cylinders H9 and H0,respectively, formed on top andbottom heads and which are individualtothe relief valve portion of said combination valve 2?.

The cylinder i is is provided with a central bore l2! which receives apiston l2? which abuts mal condition by virtue of the superchargedhydraulic fluid in the line 10, which is fifty pounds pressure and whichis delivered by the pump I04 (Fig. 3) to reducing valve I06 as abovedescribed. This s'upercharged fluid acts through the two centeringpistons H and 12 to center the cage 4'1. When cage 41 is centered, theswash plate 3'! will be in its perpendicular or neutral position underthe influence of the piston I and piston rod 42 and actuating piston 43.In other words, the fluid output of pump I! will be zero.

Assuming now that the operator wishes to start the vehicle, he willoperate the control rod 46 and the direction of operation thereof willpredetermine the direction of operation of the vehicle, since it can beoperated either forwardly or reversely. The extent to which the operatormoves the rod 46 will determine ultimately the pressure of the hydraulicsystem, since the speed of the vehicle will increase from zero untilthis predetermined pressure is developed in the line.

Assuming that the operator moves the control rod 46 the maximum amountin either direction, the action will be the same except that in oneinstance the swash plate will automatically adjust itself to drive thevehicle in one direction and in the other case it will operate to drivethe vehicle in the other direction; reverse conditions producingpressure in the passageways 30 and 3!, respectively, the otherpassageway in each instance being the return passageway.

Assuming that the rod 45 therefore is moved to the maximum amount, theoutput of pump ill will be progressively increased by adjusting theswash plate 3'! automatically until the pressure in the system reaches apredetermined value which is preferably at approximately 1200 pounds persquare inch. In other words, if the rod 46 is moved a maximum amount,the swash plate "1 will be automatically adjusted by its controlmechanism including the piston 43 and the control therefor until itreaches a maximum output and this maximum output will continue to bedelivered until a pressure of 1200 pounds, for example, is reached inthe output circuit of pump I? and the input circuit of motor I 9 whichis also reflected in the control conduit 10. If rod 46 is moved onlypart way, pump 11 will start reducing its output at a correspondinglylower pressure and reach zero at a lower pressure.

If the power absorbed by the pump I1 continues to build up the pressureabove 1200 pounds, and the control rod 46 is maintained in a maxi mumposition, the swash plate 31 will be auto matically controlled by itspiston 43 to decrease progressively the fluid output of pump I1 until1800 pounds pressure is developed in the system, at which value theswash plate 31 will have been returned to its normal position and theoutput of the pump I? will be substantially zero. In other words, untitlthe output pressure is 1200 pounds per square inch the output of thepump ll will be at a maximum for maximum operation of rod 46. After thispressure is reached in the system, the output of pump l'i will beprogressively decreased until a pressure of 1800 pounds per square inchis reached, when the pump ll will be centered and its outputsubstantially zero. Obviously the range indicated is only illustrativeand either limit may be raised or lowered, though the range is apractical one which has been demonstrated in operation to be quitesuccessful.

Considering now the action of the motor l9, its

normal condition is with the swash plate substantially as illustrated,which is substantially its minimum displacement per revolution or, inother words, its highest speed condition since it delivers the greatestspeed for a given rate of fluid delivery under these conditions. Thismaximum speed or minimum consumption condition is maintainedautomatically until the pressure in the system reaches a predeterminedvalue which is preferably approximately 500 pounds per square inch. Ifthe pressure in the system builds up above 500 pounds per square inch,the swash plate 80 is automatically adjusted by its control mechanismincluding the piston 86 and its control as previously described, toincrease the consumption of the motor I9 for each revolution, or, inother words, to decrease the speed thereof for any given rate of oildelivery until the swash plate 88 is in its maximum deflected positionand the motor I 9 is consuming the maximum amount of oil per revolutionat a pressure of approximately 1200 pounds per square inch.

It is to be noted that this is the pressure at which the pump l1 startsto reduce its output. Therefore, if the vehicle is starting under a veryheavy load or encounters a very heavy load condition, with the lever 45adjusted to the maximum, the first thing that will happen will be forthe motor l9 to increase its volume of oil consumed per revolution andthus decrease its speed until a pressure of 1200 pounds per square inchis developed in the system where its consumption per revolution will beat a maximum. Thereafter, as the force which the vehicle must overcomeincreases, the output of the pump ll will progressively decrease whileits pressure progressively increases. The decrease in fluid output will,of course, decrease the speed of travel of the vehicle, while theincrease in pressure in the system will increase the torque of the motorl9. As a con sequence the vehicle will be a good hill climber or havegood starting characteristics under a heavy load, or be a good pusherbecause the transmission will develop maximum torque at minimum speed.For this reason, the novel hydraulic transmission is particularlyadapted for such de vices as loading machines which require considerablepushing force to push them into coal; kerf cutters which may be eitherwheel mounted or cable controlled which require a large pushingorpulling force to feed the cutter into the coal and shuttle cars whichmay when heavily loaded require very high starting torque at low speed.

The transmission is also well. adapted for use in undergroundlocomotives, particularly those which are usedfor gathering, and forstarting under a very heavy load which requires a condition of hightorque at low speed. It is obvious that other vehicles which require ahigh torque at low speed may advantageously employ the hydraulictransmission of my invention.

It may further be pointed out that in many of these machines in whichthis apparatus may be employed, it is extremely desirable that the hightorque be developed without requiring a high speed, since it is adesirable characteristic of many machines to have them slow down whenthey encounter a strong resisting force and develop a very high torqueat the low speed so as to overcome the resisting force gradually.

The other features of the invention. were helieved to be fully describedheretofore and will not be repeated.

Obviously those skilled in the art may make various changes in thedetails and arrangement of parts without departing from the spirit andscope of the invention as'defined by the claims hereto appended, and Itherefore wish not to be restricted to the precise construction hereindisclosed.

Having thus described and shown an embodiment of my invention, what Idesire to secure by Letters Patent of the United States is:

1. A hydraulic transmission including a reversible variable volumehydraulic pump including an adjustable member having a normal settingfor causing said pump to deliver substantially zero output of hydraulicfluid and adjustable to cause reverse flow of fluid at any one of a plu-'rality of preselected output pressures while driven in the samedirection, a hydraulic motor connected to receive hydraulic fluid fromsaid pump and operable in reverse directions in response to reverse flowof hydraulic fluid from said pump, said motor including an adjustablemember having a normal setting causing said motor to operate at a highspeed at low input volume and adjustable to increase the input volumeand decrease the speed of the motor in response to high output pressureof said pump, means for adjusting the adjustable member of said motor asaforesaid including a servomotor, a control valve operable when in itsneutral position to lock said servomotor and when in reverse position toproduce reverse movement of said servomotor, control means for saidvalve including link-age mechanism having a control member associatedtherewith, said linkage mechanism being operated by the position of saidservomotor and the position of said control member, a spring urging saidcontrol member toward a position in which said valve causes saidservomotor toadjust said adjustable member to its said normal position,hydraulically operated means responsive to the output fluid pressure ofsaid pump for opposing the action of said spring and urging said controlmember toward a position in which said valve causes said servomotor toadjust said adjustable member from its normal position to a adjustedposition for delivering any one of said preselected output pressures,said means including a servomotor, a controlvalve operable when in itsneutral position to lock said servomotor and when in reverse position toproduce reverse movement of said servomotor, control means for saidcontrol valve including linkage mechanism having a control memberassociated therewith, said linkage mechanism being operated by theposition of said servomotor and the position of said control member, amanually operable member, a spring interconnecting said control memberand said manually operable member whereby said spring urges said controlmember in one direction with a 'force determined by the position of saidmanually operable member, and hydraulically operated means responsive tothe output fluid pressure of said pump for opposing the action of saidspring on said control member when said manually operable member isshifted in either direction from that position in which it requires theadjustable member of said pump to be in its said normal zero output.position thereby adjusting said servomotor valve for controlling theposition of the adjustable mem- 16 her of said pump in response tothe'output fluid pressure of said pump.

2. A hydraulic transmission including a reversible variable volumerotary hydraulic pump in cluding an adjustable swash plate having a normal setting for causing said pump to deliver substantially zero outputof, hydraulic fluid and adjustable to cause reverse flow of fluid at anyone of a plurality of preselected output pressures while driven in thesame direction, a rotary hydraulic motor connected to receive hydraulicfluid from said pump and operable in reverse directions in response toreverse flow of hydraulic fluid from said pump, said motor including anadjustable swash plate having a normal setting causing said motor tooperate at a high speed at I low input volume and adjustable to increasethe input volume and decrease the speed of the motor in response to highoutput pressure of said pump, means for adjusting said motor swash plateas aforesaid including a servomotor, a control valve operable when inits neutral position to lock said servomotor and when in reversepositions to produce reverse movement of said servomoton'control meansfor said valve including linkage mechanism having a control shellassociated therewith, said linkage mechanism being operated by theposition of said servomotor and the position of said control shell, aspring in said shell urging it toward a position in which said valvecauses said servomotor to adjust said motor swash plate to its normalposition, hydraulically operated piston means responsive to the outputfluid pressure of said pump for opposing the action of said spring andurging said shell toward a position in which said valve causes saidservomotor to adjust said motor swash plate from its normal position toa position in which the input volume of said motor is increased and itsspeed decreased, means for reversibly adjusting said pump swash plate tovarious positions and looking it in adjusted position for delivering anyone of said preselected output pressures, said means including aservomotor, a control valve operable when in its neutral position tolock said servomotor and when in reverse positions to produce reversemovement of said servomotor, control means for said control valveincluding linkage mechanism having a control shell asso-- ciatedtherewith, said linkage mechanism being operated by the position of saidservomotor and. the position of said control shell, a manually operablelongitudinally movable rod extending into said shell, a springinterconnecting said shell and said rod whereby said spring urges saidshell in one direction with a force determined by the position of saidrod, and a pair of hydraulically operated pistons each responsive to theoutput fluid pressure of said pump, one of which pistons opposes theaction of said spring on said shell when said rod is shifted in eitherdirection from that position in which it requires said pump swash platetobe in its said normal zero output position thereby adjusting saidservomotor valve for controlling the position of the pump servomotor andswash plate in response to the output fluid pressure of the pump.

3. A hydraulic transmission including a reversible variable volumehydraulic pump having a pair of ports functioning selectively as inputand output ports for said pump, said pump also including an adjustablemember having a normal setting for causing said pump to deliversubstantially zero output of hydraulic fluid and adjustable to causereverse flow of fluid at any one 1? of a plurality of preselected outputpressures while driven in the same direction, a hydraulic motor having apair of ports, separate conduit means connecting each of said pump portswith one of said motor ports whereby said motor receives hydraulic fluidfrom and discharges hydraulic fluid to said pump and is operable inreverse directions in response to reverse flow of hydraulic fluid, saidmotor including an adjustable member having a normal setting causingsaid motor to operate at a high speed at low input volume and adjustableto increase the put Volume and decrease the speed or the motor inresponse to high output pressure of said pump, means for adjusting theadjustable member of said motor as aforesaid including a servomotor, acontrol valve operable when in its neutral position to lock saidservomotor and when in reverse position to produce reverse movement ofsaid servomotor, control means for said valve including linkagemechanism having a control ber associated therewith, said linkage mechansin being operated by the position of said servomotor and the positionof said control member, a spring urging said control member toward aposition in which said valve causes said servomotor to adjust saidadjustable member to its said normal position, hydraulically operatedmeans responsive to the output fluid pressure of said pump for opposingthe action of said spring and urging said control. member toward aposition in which said valve causes said servomotor to adjust saidadjustable member from its normal position to a position in which theinput volume of said motor is increased and its speed decreased, meansfor reversibly adjusting the adjustable member of said pump to variouspositions and looking it in adjusted position for delivering any one ofsaid preselected output pressures, said means ineluding a servomotor, acontrol valve operable when in its neutral position to lock said servo--motor and when in reverse position to produce reverse movement of saidservomotor, control means for said control valve including linkagemechanism having a control member associated therewith, said linkagemechanism being operated by the position of said servomotor and theposition of said control member, a manually operable member, a springinterconnecting said control member and said manually operable memberwhereby said spring urges said control member in one direction with aforce determined by the position or" said manually operable member,hydraulically operated means responsive to the output fluid pressure ofsaid pump for opposing the action of said spring on said control memberwhen said manually operable member is shifted in either direction fromthat position in which it requires the adjustable member of said pump tobe in its said normal zero output position thereby adjusting saidservomotor valve for controlling the position of the adjustable memberof said pump in response to the output fluid pressure of said pump,brake means for said motor operative when the adjustable member oi saidpump is adjusted to its normal position. for causing said pump todeliver substantially zero output of hydraulic fluid including a valveadapt ed to connect said conduit means extending between said pump andmotor ports, said valve including a pressure responsive operatingmechanism adapted to open said valve in response to a preselectedpressure, and conduit means including a pressure shiftable valveconnecting said pressure responsive operating mechanism to that 18conduit receiving hydraulic fluid from said motor and manually operatedmeans for opposing said pressure operating mechanism whereby said motormay be braked when the pressure in the conduit to which it isdischarging exceeds said predetermined pressure.

4. A hydraulic transmission including a reversible variable volumerotary hydraulic pump having a pair of ports functioning selectively asinput and output ports for said pump, said pump also including anadjustable swash plate having a normal setting for causing said pump todeliver substantially zero output of hydraulic fluid and adjustable tocause reverse flow of fluid at any one of a plurality of preselectedoutput pressures while driven in the same direction, a rotary hydraulicmotor having a pair of ports, separate conduit means connecting each ofsaid pump ports with one of said motor ports whereby said motor receiveshydraulic fluid from and discharges hydraulic fluid to said pump and isoperable in reverse directions in response to reverse flow of hydraulicfluid from said pump, said motor including an adjustable swash platehaving a normal setting causing said motor to operate at a high speed atlow input volume and adjustable to increase the input volume anddecrease the speed of the motor in response to hi h output pressure orsaid pump, means for adjusting said motor swash plate as aforesaidincluding a servomotor, a control valve operable when in its neutralposition to lock said servomotor and when in reverse position to producereverse movement of said servomotor, control means ior said valveincluding linkage mechanism having a control shell associated therewith,said linkage mechanism being operated by the position of said servomotorland the position of said control shell, a spring in said shell urgingit toward a position in which said valve causes said servomotor toadjust said motor swash plate to its normal position, hydraulicallyoperated piston means responsive to the output fluid pressure of saidpump for opposing .the action of said spring and urging said shelltowarda position in which said valve causes sa'id servomotor to adjustsaid motor swash plate from its normal positionto a position in whichthe input volume of said motor is increased and its speed decreased,means for reversibly adjusting said pump swash plate to variouspositions and locking it in adjusted position for delivering any one ofsaid preselected output pressures, said means including a servomotor, acontrol valve operable when in its neutral position to lock saidservomotor and when in reverse position to produce reverse movement ofsaid servomotor, control means for said control valve including linkagemechanism having a control shell associated therewith, said linkagemechanism being operated by the position of said servomotor and theposition of said control shell, a manually operable longitudinallymovable rod extending into said shell, a spring interconnecting saidshell and said rod whereby said spring urges said shell in one directionwith a force determined by the position of said rod, a pair ofhydraulically operated pistons each responsive to the output fluidpressure of said pump, one of which pistons op poses the action of saidspring on said shell when said rod is shifted in either direction fromthat position in which it requires said pump swash plate to be in itssaid normal Zero output position thereby adjusting said servomotor valvefor controlling the position of the pump servomotor and swash plate inresponse to the output fluid 19 pressure of the pump, brake means forsaid motor operative when said pump swash plate is adjusted to itsnormal zero output position including a valve adapted to connect saidconduit means extending between said pump and motor ports, said valveincluding a pressure responsive operating mechanism adapted to open saidvalve in response to a predetermined pressure, and conduit meansincluding a pressure shiftable valve connecting said pressure responsiveoperating mechanism to that conduit receiving hydraulic fluid from saidmotor and manually operated means for o'pposingsaid pressure operatingmechanism whereby said motor-.may be braked when the pressure in theconduit to which it is discharging exceeds said" predetermined pressure.

5. A hydraulic transmission including a reversible variable volumehydraulic pump having a pair of ports functioning selectively as inputand output ports for saidpump, said pump also including an adjustablemember having a normal setting for causing said pump to deliversubstantially zero output of hydraulic fluid and adjustable to causereverse flow of fluid while driven in the some direction, a hydraulicmotor having a pair of ports, separate conduit means connecting each ofsaid pump ports with one of said motor 7 ports whereby said motorreceives hydraulic fluid from and discharges hydraulic fluid to saidpump and is operable in reverse direction in response to reverse flow ofhydraulic fluid, brake means for said motor operative when theadjustable member is in its said normal setting causing said pump tohave zero output including a valve adapted to connect said conduit meansconnecting saidzpump and motor ports, a pressure responsive operatingmechanism adapted to open said valve in response to a predeterminedpressure, conduit means including a pressure shiftable valve connectingsaid pressure responsive operating mechanism to that conduit receivinghydraulic fluid from said motor, and manually operated means for opposinsaid pressure operating mechanism whereby said motor may be braked whenitsdischarge pressure exceeds said predetermined pressure.

6. A hydraulic system including a variable volume reversible outputhydraulic pump and a hydraulic motor adapted to be reversely driven bysaid pump, conduit means connecting said pump to deliver its output tosaid motor and to deliver exhaust fluid from said motor to said pump,means for adjusting said pump to have substantially zero output ofhydraulic fluid, and means for operating said hydraulic motor as abraking device, said means including a valve, mechanism for operatingsaid valve to interconnect said conduit means including means responsiveto hydraulic pressure in said exhaust conduit, an operating handle forvarying the braking action of said valve, and a pressure relief valvemeans for interconnecting said conduits in response to excessivehydraulic pressure in one of said conduit means.

7. A hydraulic system including a variable volume reversible outputhydraulic pump and a hydraulic motor adapted to be reversely driven bysaid pump, conduit means connecting said pump to deliver its output tosaid motor and to deliver exhaust fluid from said motor to said pump,means for adjusting said pump to have substan- 2o tially zero output ofhydraulic fluid, and means for operating said hydraulic motor as abraking device, said means including a valve, mechanism 1 for operatingsaid valve to interconnect said conduit means including means responsiveto hydraulic pressure in said exhaust conduit, and an operating handlefor varying the braking action of said valve. 1

8. A hydraulic system including a hydraulic pump and a hydraulic motor,conduit means connecting said pump to deliver'its output to said motorand to deliver exhaust fluid from said;

motor to said pump, means for adjusting said pump to have substantiallyzero output of hydraulic fluid, and means for operating said hydraulicmotor as a braking device, said means including a valve, mechanism foroperating said valve to interconnect said conduit means including means,responsive to hydraulic pressure in said exhaust conduit, an operatinghandle for varying the braking action of said valve, and a pressurerelief valve means for interconnecting said conduits in response toexcessive hydraulic pressure in one of said conduit means.

9. A hydraulic system including a hydraulic pump and a hydraulic motor,conduit means connecting said pump to deliver its output to said mootrand to deliver exhaust fluid from said motor to said pump, means foradjusting said pump to have substantially zero output of hydraulicfluid, and means for operating said hydraulic motor as a braking device,said means including a valve, mechanism for operating said valve tointerconnect said conduit means including means responsive to hydraulicpressure in said exhaust conduit, and an operating handle for varyingthe braking action of said valve.

10. A hydraulic system including a hydraulic pump and a hydraulic motor,conduit means connecting said pump to deliver its output to said motorand to deliver exhaust fluid from said motor to said pump, and means foroperating said hydraulic motor as a braking device, said means includinga valve, mechanism for operating said valve to interconnect said conduitmeans including means responsive to hydraulic pressure in said exhaustconduit, and an operating handle for varying the braking action of saidvalve.

STERLING C. MOON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,111,994 Ciarlo Sept. 29, 19141,172,412 Von Saalfeld Feb. 22, 1916 1,299,751 Magie Apr. 8, 19191,609,833 Robson Dec. 7, 1926 1,762,534 Sorensen June 10, 1930 1,779,757*Streckert Oct. 28, 1930 1,840,866 Rayburn et a1. Jan. 12,1932 2,161,439Thoma June 6, 1939 2,205,647 Ferris June 25, 1940 2,229,419 Merrill Jan.21, 1941 2,257,724 Bennetch Oct. 7, 1941 2,280,875 Wahlmark Apr. 28,1942 2,420,155 Tucker May 6, 1947 2,554,047 Moon May 22, 1951

